Electron discharge device



Feb. 22, 1949.

w. v'. SMITH ELECTRON DISCHARGE DEVICE Filed Feb. 26, 1946 2 Shets-Sheet1 F/Gi/ {g so Feb. 22, 1949. V w. v. SMITH 2,462,137

ELECTRON DISCHARGE DEVICE Filed Feb. 26, 1946 2 Sheets-Sheet 2 F/GZ.

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Patented Feb. 22, 1949 I ELECTRON DISCHARGE DEVICE William V. Smith,Medford, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass,a corporation of Delaware Application February 26, 1946, Serial No.650,358

6 Claims.

This invention relates to electron-discharge devices, and moreparticularly to such devices as are known as magnetrons.

This invention is particularly suitable for tuning or frequencymodulation magnetrons which are adapted to generate microwaves having awavelength of the order of several centimeters or less.

An object of this invention is to produce such a device in which thefrequency of the oscillations may be modulated over an extremely wideband, for example, megacycles or more.

Another object is to devise such an arrangement in which the energyrequired to produce the frequency modulation is reduced to a smallvalue.

A further object is to devise such an arrangement in which the currentflow in the modulating circuit is very small.

The foregoing and other objects of this invention will be bestunderstood from the following description of exemplifications thereof,reference being had to the accompanying drawings wherein:

Fig. 1 is a fragmentary, longitudinal section of an electron-dischargedevice incorporating the invention;

Fig. 2 is a fragmentary, transverse section taken along line 2-2 of Fig.1.

Fig. 3 is a fragmentary, perspective view with certain parts broken awayshowing the relationship of one of the modulating electrodes withrespect to the anode arms; and

Figs. 4 and 5 are circuit diagrams representing two typical modulatingcircuits.

The arrangement as shown in Figs. 1 and 2, illustrates a magnetronindicated generally by the reference numeral I. This magnetron includesan anode structure 2, a cathode structure 3, a magnetic means 4 forestablishing a magnetic field in a direction generally perpendicular tothe electron path between said cathode and anode structures and a pairof modulating elec- The anode structure 2 preferably comprises acylindrical body I made of a highly conductive material such as copperand provided with a plurality of anode members in the form of interiorlyextending, radially disposed vanes 8. The cylindrical body 1 is closedat its end by plates 9 and ill, the junction between said body and saidplates'being hermetically sealed as by silver solderin The c lindricalbody 1 is of such diameter and the number, size and relative spacing ofthe vanes 8 are so chosen that each pair -2 of adjacent vanes, togetherwith that portion of said cylindrical body lying therebetween, defines acavity resonator adapted to oscillate in the desired frequency range.

The cathode structure 3, which is coaxial with the anode structure 2,preferably comprises an elongated sleeve I l, conventionally made ofnickel or the like, and having a reduced portion I2 which issubstantially coextensive with the vertical dimension of the vanes 8 andprovided with a highly electron-emissive coating, for example, of thewell known alkaline earth metal oxide type. In order to support thecathode sleeve ll with respect to the anode members 8, said sleeve maybe reduced at its lower end to fit into a tubular conducting member l3adapted to be supported from a tubular pole piece I hermetically sealedinto the end plate 9. The pole piece M is provided with a bore Illathrough which the cathode structure may enter the device. A sleeve l5 ofa metal which seals well with glass is sealed in the lower end of thepole piece M. A glass sleeve I6 is sealed to the lower end of the sleevel5 and in turn is sealed to and carries av metal sleeve H. The lower endof the tubular member [3 is electrically connected and supported by thesleeve I! in any desired manner not shown. The cathode sleeve H may beheated by a filament not shown connected at one end [8 to said sleeveand at the other end to a lead-in conductor l9 suitably entering saiddevice through a glass seal not shown in the lower end of the sleeve l1.

Current may be conveyed to the heating filament by connecting anappropriate source of Voltage between the member I! and the lead-inconductor l9.

Another pole piece 20 is hermetically sealed. into the end plate ill.The pole piece 20 is likewise provided with a bore 20a terminating in atubular member 2! sealed in the upper end thereof. The device is adaptedto be evacuated through said tubular member which is then sealed at itsupper end. The pole pieces 20 and I l are fixed, for example, at theopposite ends of a horseshoe magnet not shown, the two Dole pieces andthe horseshoe magnet constituting the above-mentioned magnetic means 4for establishing a magnetic field transverse to the electron pathbetween the cathode and anode structures of the device.

The modulating electrodes 5 and 6 are supported adjacent the upper andlower open ends of the cavity resonators. The surfaces facing these openends are preferably so constituted as to be good secondary electronemitters. For exductor 22 passing out of the device through a.-

pipe 23 threaded and hermetically sealed in the cylindrical body l. Theouter :end of the. conductor 22 passes through a glass seal 24-carriedcby the outer end of said pipe 23. Likewise; the electrode 6 is supportedby a conductor 25.which passes out through a pipe 26 and a glass sleeve21 similar to those described in connecti0n-with-- the electrode 5.

When the device is generating oscillations, these oscillations may belet out therefrom by means of a loop 28 introduced into one of. thecavity resonators, said loop being supported by apipe 29 threaded andhermetically sealed in the cylindrical body 1. One end of the loop 28is-connected' to the inner end of said pipe and the other end passes outthrough a glass sleeve Elli-supported at the outer end of said p pe.

As illustrated in Fig. 4, the cathode 3 may be maintained at the propernegative potential by a source of such potential illustrateddiagrammatically as a battery 3!. Pursuant to this in-,- vention it isdesirable that the electrodes 5 and 6- be' biased negatively withrespect to the anode :2

structure 2. For this purpose biasing sources of potential illustrateddiagrammatically as batteries 32 and 33 may be interposed between theelectrodes 5 and 6 and the anode structure 2. In series with one of thesources of biasing potential may be placed a suitable source ofmodulating voltage 34. The maximum amplitude of this modulating voltageis preferably related to the biasvoltage 33 so that the electrode 6never becomes appreciably positive during operation. In a particularembodiment in which the voltage 3| was about 1200 volts, the voltage 32about 500 volts, the voltage 33 about 250 volts and the modulationvoltage having an amplitude between its maximum positive and negativepeaks of about 500volts, the frequency at which the device oscillatedcould be varied through a range of about 15 megacycles.

In accordance with my present understanding of the theory of operationof this device, I believe that the operation is substantially asfollows. In the space immediately adjacent either of the electrodes 5and 6, will be found some free electrons whether due to the emissionfrom the oathode 3 or from some other source. These electrons will beimpelled under the voltage existing between the electrode 5 for exampleand the anode 2"in a direction toward the open ends of the cavityresonators. The device which under these conditions will be generatingoscillations will have produced between the outer ends of the vanes 8 ahigh voltage, high frequency electrical field. Therefore, as theelectrons enter this region they will be subjected to the action of thelongitudinal magnetic field as well as the action of the transverse highfrequency electrical field. Under these conditions, the electrons willtravel in a variable spiral path toward the lower open end of the theelectrons from being captured by the surfaces of the vanes 8. As theelectrons in a particular cavity emerge from the lower end thereof,those electrons which are in proper phase relation with respect to thehigh frequency electrical field will have imparted thereto aconsiderable acceleration. If there were no electrode such as 6,interposed in their path, these electrons would be quickly captured, forexample, by the pole piece [4 or by the cover 9. However, the electrode6 which is interposed in the path of these electrons will interceptthem. The acceleration to which these electrons are subjected by thehigh frequency electrical field :will be suflicient to cause them toliberate large numbers of secondary electrons from the electrode 6.These secondary electrons will .be impelled by the bias voltage existingbetween the electrode and the anode structure-in adirection to reenterthe cavity resonator. Those electrons which are not in proper phase withrespectto the high frequency electrical field,

as they tend to emerge. from thelower end of, the

cavity resonator, will be deceleratedand willjree enter the cavityresonator. thus joining with the .1 secondary electrons emitted fromtheelectrodefi.

in their travel through the cavity resonator in an upward directiontoward the electrode 5. At the upper end of the anode structure asimilar action occurs as the electrons emerge from the; cavityresonators thus producing a large amount of secondary emission from theelectrode 5. Under; these conditions, an electron multiplying action-is.

created between the electrodes 5 and 6 which reeach of the cavityresonators.

the space within each of' the cavity resonators and thus, by varying-thedensity of this electron.

population, the frequency at which the cavity trolled.

oscillating circuit thus imparting to the device a 1 relatively highefiiciency.

By varying the extent to which the electrons between either or both ofthe electrodes 5 and 8 and the anode 2 are reflected into the cavityresonators, the densityof'the electron concentration in the cavityresonators readily may be controlled. Thus, for example, by interposingthe modulation voltage 34 in the connection extending to the electrode5, the frequency modulation described above may be obtained.

Electrons which pass directly from either of the electrodes 5 and B tothe upper ends of the vanes 3 constitute an ineffective flow of currentand thus it is desired that such flow be reduced to a minimum. For thispurpose, electrodes 5 andfi may'each be provided with an electricalshielding member 35 supported by each of said electrodes. This shieldingmember 35 is provided with a plurality of inwardly extending radial armswhich are closely spaced" from and substantially cover those uppersurfaces of the vanes 8 which tend to intercept the electrons. In thisway the electron flow is constrained to pass between the anode arms 81Although both of the electrodes 5 and 6 have been described as beingelectron emissive, in some instances one of these electrodes may be thusconstituted, the other electrode serving sole- 1y as an electronreflecting member. However,

under these conditions, a substantial amount of frequency modulation maylikewise be obtained Instead of modulating the voltage on but one of theelectrodes 5 and 6, various other circuit arrangements may be devised.For example, in Fig. 5 there is illustrated an arrangement in which thevoltage on both of these electrodes is modulated. The electrodes 5 and 6may be connected together and a connection extending from the commonlead to the anode structure may include a biasing battery 36 and asource of modulation voltage 31. In this instance likewise the biasingbattery 36 is so polarized as to tend to maintain the electrodes 5'and 6negative with respect to the anode structure 2. Such an arrangementlikewise produces the desirable frequency modulation.

Although the electrodes 5 and 6 have been indicated as being sources ofsecondary electrons, other types of electron sources may be utilized.

For example, either one Or both of the electrodes 5 and 6 may be heatedto temperature of thermionic emission. Under these conditions also theshielding member 35 effectively reduces the current flow and drivingpower required in the modulating circuit.

Of course it is to be understood that this invention is not limited tothe particular details as described above inasmuch as many equivalentswill suggest themselves to those skilled in the art.

What is claimed is:

1. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and including a pair of anode arms which,together with that portion of the anode structure lying therebetween,defines a cavity resonator open at both ends, a source of electronsfacing one of said open ends, an electron-reflecting electrode facingthe other of said open ends, and means adjacent said source of electronsfor shielding the surfaces of the anode arms from electrons emitted fromsaid source.

2. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and including a pair of anode arms which,together with that portion of the anode structure lying therebetween,defines a cavity resonator open at both ends, a pair of electrodesfacing said open ends, one of said electrodes being electron emissiveduring operation, and means adjacent last-named electrode for shieldingthe surfaces of the anode arms from electrons emitted from saidlast-named electrode.

3. An electron-discharge device comprising a 6 cathode, an anodestructure spaced from said cathode and including a pair of anode armswhich, together With that portion of the anode structure lyingtherebetween, defines a cavity resonator open at both ends, a pair ofelectrodes facing said open ends, one of said electrodes having asecondary electron-emissive surface, and means adjacent said last-namedelectrode for shielding the surfaces of the anode arms from electronsemitted from said last-named electrode.

4. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and including a cavity resonator open at itsends, a source of electrons facing one of said open ends, anelectron-reflecting electrode facing the other of said open ends, andmeans intermediate said source of electrons and said anode structure forshielding the surfaces of said anode structure facing said source ofelectrons from electrons emitted from said source.

5. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and including a pair of anode arms Which,together with that portion of the anode structure lying therebetween,defines a cavity resonator open at both ends, a source of electronsfacing one of said open ends, an electronreflecting electrode facing theother of said open ends, and a pair of metallic fingers depending fromsaid source of electrons and interposed between said source and theadjacent surfaces of said anode arms.

6. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and including a pair of anode arms which,together with that portion of the anode structure lying therebetween,defines a cavity resonator open at both ends, a source of electronsfacing one of said open ends, an electronreflecting electrode facing theother of said open ends, and a shielding member supported intermediatesaid source of electrons and the adjacent surfaces of said anode armsfor shielding the latter from electrons emitted from the former.

WILLIAM V. SMITH.

REFERENCES CITED Name Date Schmidt Dec. 31, 1946 Number

